The present invention relates to a method and apparatus for examining a body. The invention is particularly useful in tomography for producing transverse sectional images of the body being examined, and is therefore described below with respect to this application.
Computerized axial tomographic (hereinafter called "CAT") apparatus is known which reconstructs an image of a body being examined by rotating a source of penetrating radiation, e.g., X-rays, completely around the body. Typical apparatus includes a carriage, generally in the form of a U-shaped yoke. The radiation source is supported on one leg of the yoke, and the detector means on the other leg, the yoke being driven through a plurality of linear (i.e., rectilinear) traverses, each at a different angular position with respect to a circle, known as the circle of reconstruction within which the body to be examined is located. Some apparatus, known as LRM (linear-rotational-mode) apparatus, may be operated both according to the above linear mode and also according to a rotational mode to provide a fast rotational traverse of the radiation source and detector means around the circle of reconstruction within which the examined body is located.
It is critical to maintain a fixed spatial relationship between the radiation source and the detector means during their traverse of the examined body. For this reason, existing LRM apparatus usually includes a plurality of high-precision parallel slides guiding the linear movement of the carriage. Such slides are expensive to provide, and time-consuming to align.
In addition, the radiation from the source in such apparatus is usually of a fan-beam shape. The length of each traverse of the carriage must therefore be sufficient for the fan-beam to clear the circle of reconstruction while travelling at a constant velocity and while also providing sufficiently for stop and reverse motions for the carriage. Accordingly, the length of traverse of the carriage must increase with fan angle, source distance from center, and linear speed. Since each linear traverse is made at a different angular position around the examined body, the apparatus must necessarily be of large size to enable the carriage to clear the ground at the extreme angular positions of the carriage.
Because of the foregoing and other considerations, the CAT apparatus, particularly of the LRM type now in use, is designed according to a compromise between speed and size, high speed being desirable in order to reduce the scanning time but also requiring bulky constructions expensive to produce, difficult to maintain and noisy in operation.